Develop Reference

window.webContents.send() causes memory leak

I'm experiencing an issue in Electron where window.webContents.send() behaves as expected on the first execution, but after I call it again the function runs twice, then three times, etc.
Here's a stripped back example of one of the menubar functions I'm using to tell the renderer to package data for saving.
Main.js
{
label: 'Save',
click() {
window.webContents.send('myChannel', myArgs);
}
}
Renderer.js
ipcRenderer.once('myChannel', (evt, myArgs) => {
// package data for saving
});
My understanding is that Electron is creating a new event handler each time I click save in the menubar. I can't seem to find any documentation on how to dispose the event handler in the electron docs.
Here's a link to a similar problem. The solution isn't of much help to me, as I need these functions to only be run when they're called from the menubar, not when the app first launches.
Thanks!

React Native (iOS): RCTEventEmitter before javascript is loaded

I have a problem implementing beacons in my app. I am using the library react-native-beacons-manager, but I think is a general "problem".
The issue is that when I kill my app (and this is important to reproduce the issue) and I get closer to my beacon, iOS fire an event regionDidEnter that is caught by a file wrote in native code, and then, sent to javascript using the method of RCTEventEmitter: [self sendEventWithName:#"regionDidEnter" body:event];
The problem is that this event is fired before javascript is fully loaded, so my listener:
// component.js
Beacons.BeaconsEventEmitter.addListener('regionDidEnter', b => {
//code
});
doesn't get called.
Order of events:
[BeaconsDemo] Did finish launching enter
[BeaconsDemo] Did finish launching After jsBundleURLForBundleRoot
[BeaconsDemo] Did finish launching After RCTRootView alloc
[BeaconsDemo] Did finish launching After UIWindow alloc
[BeaconsDemo] Did finish launching After makeKeyAndVisible
[BeaconsDemo] Did finish launching end
--iOS send the event and it is caught by RNiBeacon but it has no listeners yet--
[BeaconsDemo] no listeners in RnIBeacon.m
--Register
[BeaconsDemo] regionDidExit
-- First line of javascript --
[BeaconsDemo] start observing
[BeaconsDemo] requestAlwaysAuth
Any idea to handle this situation? Is there any way or approach to send the event through RCTEventEmitter waiting for the javascript is loaded?
Thanks

This general problem also exists when writing native beacon apps for iOS or Android. The solution is that you must set up your "hook" that enables beacon monitoring and adds the event listener (or delegate / notification callback as it is called in native code) in the appropriate place per platform:
iOS: AppDelegate.didFinishLanching(options: )
Android: Application.onCreate()
The key is that this setup must be complete before those methods return.
This same rule applies for ReactNative. The trick with ReactNative, is that by default JavaScript does not run on these events -- it runs only when a screen is launched, which sets up the hook too late for the above to work when your app is killed. To get this to work, you'll need to eject your app so you can set up some custom native code in the above callbacks.
Two options:
Implement beacon detection natively (easiest, but requires native coding on a per-platform basis)
Add native code in the above native callbacks that starts a RCTBridge on iOS, and launches a view that executes code that triggers our JavaScript code to set up beacon detection. On Android, the equivalent would be to construct a new ReactRootView and ReactNativeInstanceManager in a way that it triggers your JavaScript code to set up beacon detection.
I have not personally tested option 2 to see if it can set up the hooks soon enough. If it works, it will certainly be harder than the native solution, but allows you to keep your beacon detection logic in JavaScript.

(https://github.com/MacKentoch/react-native-beacons-manager/issues/50)
I've forked #newoceaninfosys' fork and added the 'missed beacon' method. Check my last 3 commits for how to replicate it.
(https://github.com/iamandiradu/react-native-beacons-manager)
Use it by adding this in your didMount function:
if (Platform.OS === 'ios') {
// iOS cold start listener
this.beaconMissedListener = Beacons.BeaconsEventEmitter.addListener(
'onMissedBeacon',
data => {
if (data) {
this._beaconListener(data);
}
},
);
Beacons.getMissedBeacon();
}
This will retrieve the data that got 'lost' because the event triggered faster than the listener.
(React Native (iOS): RCTEventEmitter before javascript is loaded)
Hope this helps someone. :)

How to know if service worker was updated in gatsby-plugin-offline

I've installed gatsby-plugin-offline, It works fine, but I want to listen for sw update event so I can notify user that new version of app is available.
Prior to this I used offline-plugin Which I speculate is behinde gatsby's plugin? They have doc explaining how to achieve what I want here: https://github.com/NekR/offline-plugin/blob/master/docs/updates.md but I can't figure out how to get these events via gatsby, any suggestions guys?

Currently gatsby-plugin-offline is a wrapper around sw-precache, and doesn't provide any direct hooks into much beyond the caching settings shown in the config options. It looks like there are a few ways around this via sw-precache, so it might be worth working on a PR or feature request over on the gatsby issues page.

I was looking for exactly the same answer.
There is an event you can hook into called "onServiceWorkerUpdateFound".
Just create (if you don't have already) a gatsby-browser.js file and do something like this.
gatsby-browser.js
exports.onServiceWorkerUpdateFound = () => {
// do something
};
I created a <div> that shows a "new version available" message with an onClick event that reloads the page (this then will activate the new service worker).
More Information: Gatsby Browser APIs

Using startTrackPage in Application Insights

I have recently been messing around with Application Insights and have been having a problem with getting the JavaScript API to work. In the default script that you are supposed to add to your page, they use the function trackPageView(). This seems to works, but I had also wanted to gather information about how long a user stayed on the page. I found the startTrackPage() and stopTrackPage() functions and tried to use those to get the information, but I always receive an error from startTrackPage().
Uncaught TypeError: appInsights.startTrackPage is not a function(anonymous function)
I have stepped through the code and the function does not seem to be created at the point I am calling it. trackPageView() is already defined though. I tried calling the function after the document loaded as well and that still failed. However, I can call it from the developer console once the page loads.
Here is where I found the information about startTrackPage() and stopTrackPage() originally. Other than that I have just been perusing around to see if anyone else has encountered this.
I appreciate the help.
Default code from App Insight:
window.appInsights = appInsights;
appInsights.startPageView();
What I have tried:
window.appInsights = appInsights;
appInsights.startTrackPage();
window.onunload = function () {
appInsights.stopTrackPage();
};

Short answer: unfortunately there's currently no way to use appInsights.startTrackPage() in the way you intend reliably.
Long answer: The reason is that startTrackPage() method is only defined in the JS that is downloaded from CDN, so until it is downloaded it is not defined.
What you could do it something like:
appInsights.queue.push(function(){appInsights.startTrackPage();})
however this would not produce correct measurement, because tracking won't start right away.
So your best approach would be record start time manually, however even that you cannot do reliably. First of all you absolutely don't want to use onunload event as at this point it will be too late for Application Insights SDK to send the data so it will most likely get lost. Using onbeforeunload and flush() will help with this problem a little bit:
var pageStart = +new Date;
window.addEventListener("beforeunload", function () {
appInsights.trackMetric("timeOnPage", (+new Date)-pageStart);
appInsights.flush();
});
However even when using onbeforeunload you are looking at high number of potential data losses - you cannot guarantee that ajax request to send data to Application Insights will complete before page navigates away and connection is interrupted. In my testing with IE was getting about 50% of losses.

How to identify first call in Cordova

I have a cordova-based app that runs on Android, iOS and Windows Phone. The starting point in my app is the index.html page, which will not only be loaded on app start, but you can redirect to it from inside the app.
I want to execute some code if and only if the app was just started (so when the index.html was displayed the first time) and not if it was redirected to it. I tried to use cookies that expire when the session ends, but cordova does not work with cookies.
Also I do not want to use session storage because some older Androids (as well as Internet Explorer) cannot handle this.
My used cordova version is 4.0.0
EDIT:
I forgot to mention that it is not a single-page app, but I use multiple pages that can be accessed, so the deviceready-event does not work, because it would be fired every time I access the index.html-page

Try smth like this:
function documentReady() {
   document.addEventListener("deviceready", handleDeviceReady, false);
}
 
function handleDeviceReady(event) {
   //cordova api is ready for use
if (!localStorage.getItem('alreadyStarted')) {
// App just started!
localStorage.setItem('alreadyStarted', true);
}
}
UPD. Also you need to set the flag at first startup (i.e. alreadyStarted = true in sessions or LocalStorage) and check it in handleDeviceReady() later.

Write to the database at first run. Everytime the app starts, check the database to see if that string is present. If it it, ignore. Else, create and write.